Insider knowledge: Understanding the influence of an insect-microbe symbiosis on pathogen vectoring

Mounting evidence suggests that symbiotic microbes can play key roles in determining infection outcomes in insect vectors, making them prime candidates for novel vector control methods. Implementing these tactics, however, requires understanding the impact of symbionts on pathogen vectoring in individual insects and their consequences for population-level disease transmission. My dissertation research focuses on the squash bug, Anasa tristis, an agriculturally important pest and a known vector of Serratia marcescens, causative agent of Cucurbit Yellow Vine Disease (CYVD). My work examines how A. tristis’ bacterial symbionts (Caballeronia) impact Serratia infection outcomes in A. tristis and how this, in turn, impacts CYVD outbreaks. Leveraging the ability to raise symbiont-free insects in the laboratory, I determined that individuals harboring symbionts have lower-intensity S. marcescens infections and are more likely to clear infection than their symbiont-free counterparts. These trends persist even when bugs are exposed to Serratia before acquiring Caballeronia. To test how these patterns play out on a larger scale, I created and parameterized a model of CYVD transmission that explicitly accounts for the presence of symbiont-positive and symbiont-free bugs. Sensitivity analyses consistently show that, in addition to the background transmission rates, the prevalence of bugs with symbionts explains a large amount of the variation in the number of infected plants we observe. Given these results, I believe future research should address the mechanisms through which Caballeronia suppresses Serratia in vivo and prioritize finding ways to manipulate symbiont prevalence in squash bug populations.